23 Aug
2005
23 Aug
'05
4:46 p.m.
In message <m1E7h9n-000IyXC at p850ug1>
ard at p850ug1.demon.co.uk (Tony Duell) wrote:
Also be aware that many HD-capcable 5.25" drives
turn at 360 rpm all the
time. Which means the data rate if you put a DD (or for that matter an
SD) disk in them is 6/5 times what you'd get with that disk in a DD drive
(which turns at 300 rpm). You may well need to provide a suitable clock
for 300 kbps, for example.
Ick. Time to find a 24MHz crystal oscillator :-/
Divide by 3 gives 8MHz, div24 for 1MHz, div48 for 500kHz, div96 for 250kHz.
And none of those are powers of two. Yay. I think I'll just stick to 8MHz and
1M/500k write clocks.
I always thought they were invented to make my job
more painful than it
should be ;-)
Only if you're trying to reverse engineer something :)
I hate ASICs too, unless they're fully documented down to gate level in some
way. The CBM 1541 is a great example... Version 1 was all TTL, v2 had an ASIC
to do the GCR coding, v3 had an ASIC that did the GCR *and* analogue
interfacing IIRC. Ick.
I still need to deal with the "only 16uS to grab a byte of data" issue.
That's going to be a major pain when the CPU is running at 2MHz... Thankfully
IDE/ATA is fairly speed independent.
I suppose I could use interrupt mode, and hijack the INT (or maybe the NMI)
vector whenever the FDD is being accessed.
Isn't learning fun?
data separators. And I've seen a board of logic
(the original IBM
controller, for example). But I've never seen a real 765 linked to an
I really should try and get a copy of the IBM PC Technical Reference manuals
at some point.
Unless you are using the original Sony 3.5"
drives, which turn at 600
rpm, and thus use twice the data rate you might expect, 5.25" drives and
3.5? drives use the same data rates for the same modes.
All new-ish PC-type floppy drives here. I don't think I've got any of the
original Sony drives - most of mine are MFD920s, with one or two MFD520s (I
prefer the 520s - they're jumperable for DS0 and ideal for RiscPCs). Some of
the Citizen drives that Acorn used are pretty well made, too - I've never
seen one that didn't work properly. Well, except for the one that some oik
(not me) shoved a mini-CD into.
HD disks (1.2Mbyte, 1.44Mbyte respectively) in their
approriate drives
use the same data rates as 8". SD and DD disks are half of those rates
_apart from the 360rpm issue I mentioned above).
Easy way to solve the 360rpm issue: Find the SPEED_SEL pin on the motor
controller, lift the pin then wire it to the edge connector.
I
FWIW, 3" are the same as those too (there never
was a HD 3" disk AFAIK).
Heh. Amstrad 3" "indestructable" floppies. Those bring back some
memories...
Mostly dealing with disintegrating drive belts.
--
Phil. | Acorn RiscPC600 SA220 64MB+6GB 100baseT
philpem at philpem.me.uk | Athlon64 3200+ A8VDeluxe R2 512MB+100GB
http://www.philpem.me.uk/ | Panasonic CF-25 Mk.2 Toughbook
... I'm spending a year dead for Tax Purposes